Obsidian

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Rock class: Extrusive Igneous Rock
Composition: Silica rich. Slot crystallization yields a light colored granite with 35% quartz, 63% feldspar and 2% ferromagnesium.
Luster: Glassy, brilliantly vitreous Hardness (Moh's Scale): 6-7 scratches window glass
Color: Black
Cleavage: Conchoidal
Environment: Volcanic. Forms through a quick cooling of silica-rich lava flow on the Earth's surface. It solidifies before minerals can develop.
Uses: In prehistoric times obsidian was used for sculptures and tools such as arrow head and knife blades.
Comments: Is an amorphous solid like window glass. [obsidianWindowGlass.jpg]

Rock class:	Extrusive Igneous Rock
Composition:	Silica rich. Slot crystallization yields a light colored granite with 35% quartz, 63% feldspar and 2% ferromagnesium.
Luster:	Glassy, brilliantly vitreous Hardness (Moh's Scale): 6-7 scratches window glass
Color:	Black
Cleavage:	Conchoidal
Environment:	Volcanic. Forms through a quick cooling of silica-rich lava flow on the Earth's surface. It solidifies before minerals can develop.
Uses:	In prehistoric times obsidian was used for sculptures and tools such as arrow head and knife blades.
Comments:	Is an amorphous solid like window glass.